1. Field of the Invention
This invention relates to the field of automatic transmissions for motor vehicles. More particularly, the invention pertains to a kinematic arrangement of gearing, clutches, brakes, and the interconnections among them in a power transmission.
2. Description of the Prior Art
A truck customer may desire improved launch capability, particularly when the vehicle is loaded and/or starting on a grade. The vehicle manufacturer offers customers options to allow improved launch capability. One option is to choose steeper (higher numerical) axle ratios. For those who have chosen a 4×4 truck, the transfer case generally is 2 speeds, one speed of which is a low-range which can also improve launch capability.
The steeper axle ratios improve vehicle launch capability when loaded, but reduce fuel economy even when the vehicle is unloaded. Offering multiple axle ratios adds complexity to the vehicle assembly plant. Operators of light trucks having 4×4 drivelines rarely use the low-range capability of a two-speed transfer case. The clutch mechanism for selecting low and high-ranges of the transfer case cannot be shifted unless the vehicle is stopped.
Most operators of such vehicle are accustomed to and prefer a small first-second gear step size of the transmission, which is 1.414 in a current production transmission. Eight-speed transmissions that have been proposed have gear mesh losses that exceeded those of highly efficient six-speed transmissions.
There is a need for a power transmission that can produce eight forward speeds and two reverse speeds, has high theoretical gear mesh efficiency and a wide speed ratio span.